A320 Gr B8M Class 2

[dozer]

Does anyone know where I could find 2" diameter threaded rod that meets ASTM A320 Gr B8M Class 2? The big problem is the mechanical requirements listed in ASTM only go up to 1-1/2" diameter but the footnote says that it's not meant to limit the size to 1-1/2". Great help that is, since they don't list a strength requirement for 2" no one wants to touch it. My feeling is if a vendor could certify that it meets the requirement shown for over 1-1/4" to 1-1/2" then that would be fine.

Failing this, does anyone know if 2" that meets same spec except B8 (304 SS) instead of B8M (316 SS) is available? Still have the same problem with the mechanical properties but I'm thinking 304 may be easier to get.

 

[theonlynamenottaken]

In similar, seemingly neverending quests for hard-to-find threaded fasteners I've found that Portland Bolt either had it, could make it, or had something that would otherwise fit the bill. Their site doesn't list 2" diameter in their A320 B8M tables, but that doesn't mean they can't make it for you.

 

[dozer]

Actually it does mean they can't make it. I asked, they said they have never come across material larger than 1-1/2" that could "hit the mechanicals of Class 2". Hey, thanks for playing though. Keep those cards and letters coming.

 

[TVP]

Here is one possibility:

B&G Manufacturing

http://www.bgmfg.com/threaded_rod_316.htm

I'm a little surprised that PB has not found a solution to this problem. Type 316 (Grade B8M) has exceptional ductility, and can be cold drawn to extremely high strengths for spring wire, so I would expect that this just requires the initial hot-rolled material to be heavily cold drawn (40% or more) prior to thread rolling. But that would entail a very large, heavily reinforced drawing die and suitable pulling capacity, which maybe doesn't exist above 2" in diameter. Universal Stainless in Dunkirk, NY and Carpenter (somewhere in PA) would be the two USA-based mills that also do cold drawing, so if you really want to explore this, you might want to contact them directly.

 

[OGMetEngr]

Here's the problem. Austenitic stainless steel can only achieve this strength level by strain hardening. More strain is induced at and near the outer surface than at the center of the fastener. As such, trying to strain harden a fastener at diameters such as this results in lower mechanical properties at the center of the fastener.

ASTM A320 Appendix X1 can explain it better than I:

X1.1 Strain hardening is the increase in strength and
hardness that results from plastic deformation below the
recrystallization temperature (cold work). This effect is produced
in austenitic stainless steels by reducing oversized bars
or wire to the desired final size by cold drawing or other
process. The degree of strain hardening achievable in any alloy
is limited by its strain hardening characteristics. In addition, the
amount of strain hardening that can be produced is further
limited by the variables of the process, such as the total amount
of cross-section reduction, die angle, and bar size. In large
diameter bars, for example, plastic deformation will occur
principally in the outer regions of the bar, so that the increased
strength and hardness due to strain hardening is achieved
predominantly near the surface of the bar. That is, the smaller
the bar, the greater the penetration of strain hardening.

 

[dozer]

Then why does ASTM A193 B8 & B8M2 Class 2B go up to 2-1/2"? Other than it states its for high temperature and A320 states its for low temperature and A320 has some impact requirements, I can't see a big difference.

Oh, and for those who are curious. We've asked our client if they will accept A193 B8M2 Class 2B. The temperature that this bolt will be at will be around -150°C. Since this is above -200°C according to A320 section 6.2.1.1 they are exempt from impact tests, so as far as I can tell it essentially meets A320.

 

[OGMetEngr]

For these A193 grades, strength is lower for each size increase shown on the table. They also have the following note at bottom of table (note D):

For diameters 1 1/2 and over, center (core) properties may be lower than indicated by test reports which are based on values determined at 1⁄2 radius.


Class 2B is probably just strain hardened to a greater degree to give a higher yield at the same size as class 2.